CA1061498A - Process for preparing polymer powders - Google Patents
Process for preparing polymer powdersInfo
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- CA1061498A CA1061498A CA257,898A CA257898A CA1061498A CA 1061498 A CA1061498 A CA 1061498A CA 257898 A CA257898 A CA 257898A CA 1061498 A CA1061498 A CA 1061498A
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/12—Powdering or granulating
- C08J3/14—Powdering or granulating by precipitation from solutions
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- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
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Abstract
ABSTRACT OF THE DISCLOSURE
A process for producing fine polymer powders which comprises dissolving 1 to 40 weight percent of a polymer in a solvent at a temperature in the range of 90 to 165°C under autogenous conditions, cooling the solution to a temperature to precipitate the polymer and to leave in solution an amount of polymer less than that which will inhibit the formation of droplets upon atomization of the solution into a drying zone, said cooling being carried out under agitation condition- of high shear, to produce a slurry of particulate polymer and solvent, atomizing said slurry into a vaporization zone, feeding a drying gas into the vaporation zone at a temperature in the range of 90 to 160°C., recovering the partially dry polymer particles, drying the particles and recovering a polymer powder of less than 100 micron size.
A process for producing fine polymer powders which comprises dissolving 1 to 40 weight percent of a polymer in a solvent at a temperature in the range of 90 to 165°C under autogenous conditions, cooling the solution to a temperature to precipitate the polymer and to leave in solution an amount of polymer less than that which will inhibit the formation of droplets upon atomization of the solution into a drying zone, said cooling being carried out under agitation condition- of high shear, to produce a slurry of particulate polymer and solvent, atomizing said slurry into a vaporization zone, feeding a drying gas into the vaporation zone at a temperature in the range of 90 to 160°C., recovering the partially dry polymer particles, drying the particles and recovering a polymer powder of less than 100 micron size.
Description
io~
This invention relates to the preparation of finely divided normally solid, synthetic organic polymeric thermo-plastic resins.
Thermoplastic polymers in powder or finely divided form have a wide variety of commercial applications, such as for example, the dry powders have been used to coat articles in dry form by dip coating in either static or fluidized beds, by electrostatic coating, spraying, or dusting and flame spraying. The powders are used in dispersed form in suitable liquid carriers to apply coatings by roller coating, spray coating, and dip coating to a variety of substrates such as glass ceramics, metal, wood, cloth, paper, paperboard, and the like. The finely divided polymers have also been success-fully employed in conventional powder molding techniques.
The fine powders have also been applied as paper pulp addi-tives, mold release agents, wax polish, paint compositions, binders for non-woven fabrics and finished for woven fabrics.
There are basically four types of processes employed in the prior art for preparing finely divided polymer par-ticles, i.e., mechanical grinding, solvent precipitation, dispersion and spray atomization of solutions or slurries.
Generally mechanical grinding employs conventional equipment to yield particles of irregular shape and wide size variation of from about 75 to 300 microns. The powders pro-duced by this method may not be suitable for applications where free flowing powders are required, since the irregular shapes may inhibit the flowability of these powders. The grinding of some polymer may be very costly because of the toughness of the resin even when cryogenically cooled.
The spray techniques are generally satisfactory for producing uniform non-agglomerated spherical particles, however, very specialized equipment, usually nozzles oper-10~14~38 ating under a limited range of conditions to prevent nozzle plugging are required. Substantial problems in spraying are the shearing of a polymer solution as it passes through the nozzle premature precipitation of the polymer or too rapid volatilization of solvent.
The dispersion method also is subject to high shear conditions. Frequently water is the dispersing medium and dispersing agents are used to facilitate the dispersion.
Hence the powders produced by this technique generally in-corporate some or all of the dispersing agent in the powder which can create undesirable changes in the original polymer properties, e.g., increased water sensitivity, loss of elec-trical insulating values, loss of adhesive capabilities, etc.
The final type of prior art process generally en-tails dissolving the polymer in a solvent, followed by pre-cipitation of the polymer in finely divided form through ~d-dition of a nonsolvent, evaporation of the solvent or a com-bination of the two. Problems in this process have included difficulty in manipulating the solvents, solvent removal, particle agglomeration which requires a great deal of grind-ing, and particles having irregular somewhat rounded shapes.
The solvent system method, however, is a relatively simple procedure for producing powders for many applications and there are a number of patents, relating to improvements.
For example, U.S. Patent 3,563,975, which discloses the prep-aration of high density polymer powders by cooling a hot solution of polymer under sufficient pressure to prevent substantial vaporization of the solvent. The patentee recognized that shear stress occurring just before the polymer is precipitated, causes polymer strings. To prevent this undesirable occurrence, an elongated cooling means was devised to precipitate polymer particles. The elongated cooling means operated with intermittent high velocity movement of material therethrough, which resulted in very little turbu-lence.
In another process described in British Patent 1,172,317 particulate powder was precipitated in a quiescent solution to avoid shear stresses and the resultant polymer strings.
Both of these processes are primarily dependent on non-turbulent precipitation of solutions during cooling, which substantially enhanced the problem of heat removal. An agitated precipitation would be far easier to cool and hence would require simplier equiyment and techniques and less time and expense than those of the prior art.
In the drawings:
Fig. 1 is a schematic representation of the process of the present invention.
Fig. 2 is a diagrammatic crystallization vessel useful for the present process.
Fig. 3 is a diagrammatic ~op view of the upper turbine of the vessel of Fig. 2.
Fig. 4 is a diagrammatic top view of the lower turbine of the vessel of Fig. 2.
Briefly stated the present invention is a process for preparing fine powders of thermoplastic polymers by dis-solving 1 up to 40 weight % of polymer, preferably at least 5 weight % in a solvent at a temperature in the range of 90 to 165C., preferably 140C. under autogenous pressure, cooling the solution with high shear agitation to a temper-ature below 90C. under autogenous pressure, while precipi-tating (or crystallizing) said polymer, to produce a slurry of particulate polymer and solvent, which is atomized into a vaporization zone into which a gas at 90 to 160 is being 10~ 8 fed, and recovering said polymer particles, having a sub-stantial portion of the solvent removed therefrom.
The agitation is quite important and may be achieved by the use of an agitator of a particular configuration as described below in detail. The agitation improves heat trans-fer and facilitates cooling the solution, thereby increasing the rate of precipitation.
In general the polymers suitable for the practice of the present invention include any normally solid synthetic organic polymeric thermoplastic resin whose decomposition point is somewhat higher than 100C. Included are polyole-fins, vinyls, olefin-vinyl copolymers, olefin-allyl copolymers, polyamides, acrylics, polystyrene, cellulosics, polyesters, and polyhalocarbons.
Generally, the most suitable polyolefins for use in the present process include normally solid poly~ers of mono-alpha-olefins, which comprise from 2 to 6 carbon atoms, for example~ polyethylene, polypropylene, polybutene, polyiso-butylenes~ poly (4-methylpentene~ copolymers of alpha-olefins and the like.
Vinyl polymers suitable for use herein include polyvinyl chloride, polyvinyl acetate, vinyl chloride/vinyl acetate copolymers, polyvinyl alcohol and polyvinyl acetal.
Among the suitable olefin-vinyl copolymers are ethylene-vinyl acetate, ethylene-vinyl propionate, ethylene vinyl isobutyrate, ethylene-vinyl alcohol, ethylene-methyl acrylate, and the like. Olefin-allyl copolymers include ethylene-allyl alcohol, ethylene allyl acetate, ethylene-allyl acetone, ethylene-allyl benzene, ethylene-allyl ether, and the like.
Examples of some specific acrylic polymers are polymethyl methacrylate, polyacrylonitrile, poly-methyl-10~98 acrylate and polyethylmethacrylate. me polyamides suitable for use include polyhexamethylene adipamide, polyhexamethylene sebacamide, and polycaprolactam.
The present process is also useful for preparing powders from solutions of mixtures of thermoplastic polymers such as ethylene vinyl acetate/polyethylene, polyethylene/
polypropylene and the like.
The present process may also be used to produce powders from a solvent reaction system wherein the polymeric material is prepared in a solvent system~ such as for example the alpha-olefin polymers, as described in numerous patents such as U.S. 2,112,300; U.S. 3,113,115; U.S. 3,197,452;
Belgian Patent 538,782 and British Patent 994,416. CataLysts are the now well known "Ziegler" variety.
Ziegler catalysts, or more particularly, certain modified Ziegler catalysts, have been found to be especially useful for polymerizing alpha-olefins. For example, a titan-ium trichloride catalyst modified with aluminum chloride having the formula TiC13.1/3AlC13. Normally, this modified Ziegler catalyst is activated with a metal alkyl such as an aluminum alkyl, and preferably with an aluminum alkyl halide having the structural formula, R2AlX or R3A12X3~ wherein R is selected from the group consisting of alkyl radicals con-taining 1 to 12 carbon atoms or phenyl or benzyl radicals, and X is a halogen atom selected from the group consisting of chlorine, bromine or iodine.
A variety of monomers may be polymerized with the Ziegler type catalysts. Any unsaturated hydrocarbon corres-ponding to the general formula R=CH=CH2, wherein R is se-lected from the group consisting of an alkyl radical hav;ng Irom one to six carbon atoms, a phenyl radical, or an alkyl substituted phenyl radical can be used. Examples of specific unsaturated hydrocarbons which can be polymerized include alpha-olefins containing 3 to 8 carbon atoms, such as propyl-ene, butene, isobutylene, pentene, isoamylene, hexene, iso-hexenes, heptene, isoheptenes, octene, isooctenes and the like.
The preferred catalyst composition for the polymer-ization of propylene comprises a modified titanium trichlor-ide having the structural formula, TiC13.1/3AlC13, activated with diethyl aluminum chloride. Ratios of diethyl aluminum chloride and titanium trichloride of between 0.3:1 and 6:1 may be advantageously used. The presence of an alkali metal halide in an amount of between 0.5 to 10 mols of an alkali metal halide per mol of reduced titanium tetrahalide, and preferably a mol ratio of from 0.8 to 5 mols of an alkali metal halide, such as sodium chloride, per mol of reduced titanium tetrahalide can be used for improving catalyst ac-tivity.
The monomers may be polymerized at moderate temper-atures and pressures with the Ziegler type catalysts des-cribed above, generally at temperatures of 0 C. to 150C., with temperatures on the order of 25 C. to 80 C. being particularly useful. A solvent such as a paraffin or cyclo-paraffin having 3 to 12 carbon atoms, may be employed for the polymerizations, however, the olefin monomer is frequently used for this purpose. The polymerizations are preferably conducted under conditions that exclude atmospheric impur-ities such as moisture, oxygen and the like.
The pressure ranges from about atmospheric pressure to about several atmospheres with pressures in excess of about 500 psi rarely being employed.
After the polymer has been produced, the catalyst is deactivated by contacting the polymeric reaction mixture 1~)ti1~98 with a material which reacts with and deactivates the cata-lyst. Such materials include, for example, lower alcohols, acetone and water.
The term polyolefins includes those materials modi-fied with materials such as the unsaturated organic acids, for example, maleic acid, muconic acid, dimethyl muconic acid, acrylic acid, methacrylic acid, vinyl acetic acid, and the like. Generally the polyolefins may be modified by from 1 to 10 weight percent of the unsaturated acid. The modifica-tion has been observed to improve the surface adhering char-acteristics of the polyolefin polymers when they are employed as surface coatings; this is particularly true of the alpha-olefins, such as polypropylene. The modifying unsaturated acids may be incorporated into the polyolefins by intimately contacting the modifier with the polyolefin in a melt or solution of the polymer in the presence of a free radical source, such as an organic peroxide or by copolymerization with another monomer followed by neutralization or partial neutralization to yield an ionomer if desired.
In the process of the present invention it is pos-sible to employ graft polymers prepared by known methods in the art, e.g., those to be found in U.S. Patents 3,177,269;
3,177,270; 3,270,090; 3,830,888; 3,862,265; British 1,217,231; British 670,562 and the like.
The preferred modifying monomers which are grafted to the backbone are C3 to C10~ preferably C3 to C6 unsatur-ated mono- and polycarboxylic-containing unsaturated acids with preferably at least one olefinic unsaturation; anhy-drides, salts, esters, ethers, amides, and nitriles, thio, glycidyl, cyano, hydroxy, glycol and other substituted deriv-atives thereof.
Fxamples of such acids, anhydrides and derivatives 10~
thereof include maleic acid, fumaric acid, itaconic acid, citraconic acid, acrylic acid, glycidyl acrylate, cyano ethyl acrylate, hydroxy ethyl methacrylate, acrylic poly-ethers, acrylic anhydride, methacrylic acid, crotonic acid, isocrotonic acid, mesaconic acid, angelic acid, maleic an-hydride, itaconic anhydride, citraconic anhydride, sodium acrylate, calcium acrylate, magnesium acrylate and the like.
Other monomers which can be used either by them-selves or in combination with one or more of the carboxylic acids or derivatives thereof include C8 to C50 vinyl mono-mers such as monovinyl aromatic compounds, i.e. styrene, chlorostyrenes, bromostyrenes, alpha-methyl styrene and the like.
Other monomers which can be used are C8 to C50 vinyl esters and allyl esters, such as vinyl butyrate, vinyl laurate, vinyl stearate, vinyl adipate and the like, monomers having two or more vinyl groups, such as divinyl benzene, ethylene dimethacrylate, triallyl phosphite, dialkylcyanur-ate and triallyl cyanurate.
The process of the present invention is especially useful for grafted polymers prepared by grafting a polymer of a C2 to C8 mono-c~-olefin or its copolymers with acrylic acid in a special process. The polymers of C2 to C8 mono- ~-olefins are commonly referred to as polyolefins and for the purpose of this invention are to include copolymers of the C2 to C8 mono-alpha-olefins with each other and with other monomers as well as the homopolymers.
Polymers containing diolefins such as butadiene and isoprene are also suitable. The polyolefins are produced utilizing in most instances a Ziegler-type catalyst, but can also be produced by Phillips catalysts and by high pressure technology.
_ g _ 10f~14~8 Examples of suitable polyolefins, both plastic and elastomeric, include low or high density polyethylene, poly-propylene~ polybutene-l~ poly-3-methyl butene-l~ poly-4-methylpentene-l~ copolymers of monoolefins with other olefins (mono- or diolefins) or vinyl monomers such as ethylene-propylene copolymers or with one or more additional mono-mers, i.e. EPDM~ethyléne/butylene copolymer, ethylene/vinyl acetate copolymer, ethylene/ethyl acrylate copolymer, propyl-ene/4-methylpentene-1 copolymer and the like.
The term "copolymer~l includes polymers formed from two or more monomer constituents and substituted derivatives thereof.
The preferred polyolefins employed in the present invention contain propylene and/or ethylene, i.e. polypropyl-ene and polyethylene. The starting polymer used as a basematerial in the graft process will preferably have a melt index (MI) (ASTM D-1238-65T) of 1 to 40, preferably 5 to 40, and most preferably 5 to 10, or melt flow rate (MFR~ between about 0.1 to 50 and preferably 0.5 to 10, most preferably 2 to 5. These melt flow rates correspond approximately to vis-cosity average molecular weights of about 100,000 to 500,000.
The preferred monomers to be grafted to the C2 to C8 polyolefin and other polymers for use in the present in-vention are maleic anhydride, acrylic acid, methacrylic acid, glycidyl acrylate, hydroxy ethyl methacrylate and their deriv-atives. Others that can be used are described elsewhere herein. However, other monomers may be added in admixture with these such as maleic anhydride (MA), styrene, acid esters, salts and the like to form graft copolymers. MA
and styrene and MA and acrylic acid are preferred over MA
alone when polymer grafts of MA are desired.
The grafting reaction is initiated by a free-radi--- 10 _ cal initiator which is preferably an organic peroxygen com-pound. Especially preferred peroxides are t-butyl perbenzo-ate, dicumyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxy-3 hexyne (Lupersol 130), alpha, alpha'-bis (tert-butylper-oxy) diisopropyl benzene (Vulcup R or Percadox 14), or any free radical initiator having a 10-hour half-life tempera-ture over 30 C. or mixtures thereof. Generally, the higher the decomposition temperature of the peroxygen compound, the better. See ~p. 66-67 of Modern Plastics, November 1971, for a more complete list of such compounds.
The free radical initiator is used in amounts cor-responding to 0.005 to 5, preferably 0.02 to 2, most prefer-ably 0.02 to 1.0 weight percent based on polymer.
The monomer to be graft polymerized is used in amounts of 0.01 to 100~ preferably 0.05 to 50~ and most pre-ferably 0.1 to 25 weight percent of the base polymer.
Generally, the monomer and initiator are blended together and added simultaneously, except in the situation of a polyethylene or ethylene predominant copolymer. Illus-trative of the graft preparation is the grafting of acrylic acid onto polypropylene. Molten polypropylene is contacted with acrylic acid at 350 to 650F., preferably 400 to 550 F.
in the presence of a peroxide initiator. The initiator and acrylic acid are added as a liquid blend. The resulting graft copolymers have been appreciably degraded and changed in molecular weight as compared to the base polymer. The solvents employed are preferably paraffins or cycloparaffins having 5 to 12 atoms. Suitable solvents include n-pentane, isopentane, n-heptane, isooctane, cyclohexane, methylcyclo-* Trade Mark.
10~
hexane, nonane, and the like or mixtures of solvents. The solvent will generally contain from about 1 to 40 weight per-cent, more preferably about 5 to 20 weight percent of polymer based on the total weight of the solution.
About 15 weight % of the polymer is dissolved in the solvent, for example n-heptane, by heating at 100 to 140C. preferably in the range of 110 to 130C. under auto-genous pressure for 5 minutes to 2 or more hours, typically about 1 hour. Preferably the temperature is selected to maintain the pressure in the autoclave at less than 75 psig;
more preferably less than 50 psig.
The slurry is produced by cooling the solution, to a temperature below 90C. Polymer precipitation begins at about 90 C. and continues as the temperature is lowered, at a rate of 1 to 10C./minute, preferably about 5C/minute.
The temperature of the solution is lowered to about 50C.
Lower temperatures may be used but are not necessary, simi-larly temperatures from 20C. up to about 80C. are suitable for the final slurry temperature. It is readily apparent that at temperatures above 20 C., somewhat larger amounts of polymer will remain dissolved in the solvent, unless long precipitation periods are provided. In any event it is neces-sary to keep the residual polymer, which is dissolved in solu-tion, below the concentration which will produce strings as the solvent is atomized along with slurry particles. Up to a critical amount of polymer may be present in solution in the solvent without the formation of strings as the solvent is atomized into a vaporization zone where the solvent is partially vaporized.
Thus since it is desirable, and one of the objects of the present invention is to remove solvent from the slurry particles, operation of the present process should be carried out such that there is less than that amount of the polymer remaining in solution in the solvent than will inhibit forma-tion of droplets at the drying zone temperature. The amount of polymer which may remain in solution in a solvent which has a vapor pressure of 50 to 400 mm of mercury at the temper-ature of the drying zone is that amount which produces a vis-cosity in the solvent of no greater than 5 centipoise at the temperature of atomi~ation. The particular lower or final precipitation temperature will have to be determined for each solvent and polymer employed to achieve this result.
This can be easily done or may be available in standard tech-nical and engineering tables in regard to some combinations.
Lengthened precipitation periods may also be used to remove larger amounts of polymer from solution at a given tempera-- 15 ture.
The cooling and precipitation is conducted in an agitated solution. As noted above, this aids cooling and speeds precipitation. However, the nature of the agitation is quite critical. The prior art believed that shearing of solution encouraged the formation of polymer strings and thus sought to avoid all agitation to prevent this unde-sirable result. However, surprisingly it has been found that high shear does not result in strings.
The apparatus used in the present process to ob-tain high shear is shown in Fig. 2. It is a vessel which isfully baffled. Turbine agitators, typically 1/3 to 2/3 the diameter of the vessel have been used, operated with good results at from 20 to 300 rpm. ~atisfactory high shear agi-tation can be obtained with paddle diameter of from 30 to ~0 percent of the internal diameter of the vessel. Figs. 3 and 4 show a top view of the turbines in Fig. 2, The degree of shearing necessary to carry out the _ 13 -process is less than that which would be achieved if an emul-sion were produced. Emulsion of the precipitated polymer would involve too high a shear and is to be avoided. Thus the present shearing may be described as less than that necessary to produce an emulsion of polymer particles in the solvent, but by conventional chemical engineering practice the agitation is intense as measured by energy input per unit volume of liquid.
The precipitated particles form a slurry in the precipitation vessel. Thus slurry is removed (by gravity, pumping, pressure, screw, etc.) and atomized through a con-ventional nozzle or centrifugal atomizing wheel such as a Niro atomiæer into a vaporization zone, into which a drying gas is being fed at a temperature of 80 to 160 C., depending on the polymer and solvent, to produce powder particles leaving the vaporization zone at temperatures generally in the range of 30 to 50C. and having about 5 to 30 weight percent solvent still associated therewith. The damp powder is then dried to completion, for example, by fluidized bed, vibrating tray, tumbling or the like.
The vaporizing gas may be air; however, explosive mixtures may result with the powder, Preferably inert gases such as nitrogen, C02, or helium are employed.
Generally, the particles produced according to this method have a size of less than 100 microns, usually over 99%
of the particles are less than 75 microns.
Some powder, for example, propylene resins (poly-propylene, ethylene-propylene copolymers, blends of propyl-enes with ethylene-propylene rubber and high density poly-ethylene and acrylic acid grafted modifications thereof hav-ing melt flow rates of 2 to 80) tend to be made of 20 to 30~/
agglomerates as taken from the vaporization zone, with the 10~i14~l~
remainder being less than lO0 microns, e.g., less than 74 microns; the average size being about 30 microns.
The agglomerates are readily reduced to finer pow-der by attrition, for example, by impingement mill (particle on particle) or pin mill, such that the yield of particles of less than 100 microns approaches 99% or more. The milled agglomerate particles are irregularly spherical, but not sharply angular or elongated as with grinding.
The usual particle size in the absence of agglo~er-ation is less than 100 microns, however~ the powders are usually classified to remove any oversized particles, e.g., agglomerates, scale, trash etc. and to separate the powders for different uses.
It has also been found that additives such as stab-- 15 ilizer3 antioxidants, coloring agents and the like may con-veniently be added to the solution of polymer, before or during precipitation and slurry stages or during or after the drying step~ Soluble or disperible additives are very evenly distributed throughout the powders.
Fig. 1 represents a schematic embodiment of appa-ratus which could be employed to carry out the present pro-cess. A vessel 10 adapted for autogenous pressure is equipped with paddle 13 operated by a motor 14 and having baffles 12.
Conduit 11~ which may be a screw conveyor is provided to feed solid polymer~ usually as pellets into the vessel 10. Line 15 is provided for solvent entry. A heating exchange means 16 is provided in the vessel 10. The following description is given in regard to a batch operation, however, the present process may be carried out by continuous and semi-continuous operation.
The solid polymer pellets are fed via conduit 11 and the solvent is fed through line 15 in the desired ratios 1 into vessel 10. It should be appreciated that the functions
This invention relates to the preparation of finely divided normally solid, synthetic organic polymeric thermo-plastic resins.
Thermoplastic polymers in powder or finely divided form have a wide variety of commercial applications, such as for example, the dry powders have been used to coat articles in dry form by dip coating in either static or fluidized beds, by electrostatic coating, spraying, or dusting and flame spraying. The powders are used in dispersed form in suitable liquid carriers to apply coatings by roller coating, spray coating, and dip coating to a variety of substrates such as glass ceramics, metal, wood, cloth, paper, paperboard, and the like. The finely divided polymers have also been success-fully employed in conventional powder molding techniques.
The fine powders have also been applied as paper pulp addi-tives, mold release agents, wax polish, paint compositions, binders for non-woven fabrics and finished for woven fabrics.
There are basically four types of processes employed in the prior art for preparing finely divided polymer par-ticles, i.e., mechanical grinding, solvent precipitation, dispersion and spray atomization of solutions or slurries.
Generally mechanical grinding employs conventional equipment to yield particles of irregular shape and wide size variation of from about 75 to 300 microns. The powders pro-duced by this method may not be suitable for applications where free flowing powders are required, since the irregular shapes may inhibit the flowability of these powders. The grinding of some polymer may be very costly because of the toughness of the resin even when cryogenically cooled.
The spray techniques are generally satisfactory for producing uniform non-agglomerated spherical particles, however, very specialized equipment, usually nozzles oper-10~14~38 ating under a limited range of conditions to prevent nozzle plugging are required. Substantial problems in spraying are the shearing of a polymer solution as it passes through the nozzle premature precipitation of the polymer or too rapid volatilization of solvent.
The dispersion method also is subject to high shear conditions. Frequently water is the dispersing medium and dispersing agents are used to facilitate the dispersion.
Hence the powders produced by this technique generally in-corporate some or all of the dispersing agent in the powder which can create undesirable changes in the original polymer properties, e.g., increased water sensitivity, loss of elec-trical insulating values, loss of adhesive capabilities, etc.
The final type of prior art process generally en-tails dissolving the polymer in a solvent, followed by pre-cipitation of the polymer in finely divided form through ~d-dition of a nonsolvent, evaporation of the solvent or a com-bination of the two. Problems in this process have included difficulty in manipulating the solvents, solvent removal, particle agglomeration which requires a great deal of grind-ing, and particles having irregular somewhat rounded shapes.
The solvent system method, however, is a relatively simple procedure for producing powders for many applications and there are a number of patents, relating to improvements.
For example, U.S. Patent 3,563,975, which discloses the prep-aration of high density polymer powders by cooling a hot solution of polymer under sufficient pressure to prevent substantial vaporization of the solvent. The patentee recognized that shear stress occurring just before the polymer is precipitated, causes polymer strings. To prevent this undesirable occurrence, an elongated cooling means was devised to precipitate polymer particles. The elongated cooling means operated with intermittent high velocity movement of material therethrough, which resulted in very little turbu-lence.
In another process described in British Patent 1,172,317 particulate powder was precipitated in a quiescent solution to avoid shear stresses and the resultant polymer strings.
Both of these processes are primarily dependent on non-turbulent precipitation of solutions during cooling, which substantially enhanced the problem of heat removal. An agitated precipitation would be far easier to cool and hence would require simplier equiyment and techniques and less time and expense than those of the prior art.
In the drawings:
Fig. 1 is a schematic representation of the process of the present invention.
Fig. 2 is a diagrammatic crystallization vessel useful for the present process.
Fig. 3 is a diagrammatic ~op view of the upper turbine of the vessel of Fig. 2.
Fig. 4 is a diagrammatic top view of the lower turbine of the vessel of Fig. 2.
Briefly stated the present invention is a process for preparing fine powders of thermoplastic polymers by dis-solving 1 up to 40 weight % of polymer, preferably at least 5 weight % in a solvent at a temperature in the range of 90 to 165C., preferably 140C. under autogenous pressure, cooling the solution with high shear agitation to a temper-ature below 90C. under autogenous pressure, while precipi-tating (or crystallizing) said polymer, to produce a slurry of particulate polymer and solvent, which is atomized into a vaporization zone into which a gas at 90 to 160 is being 10~ 8 fed, and recovering said polymer particles, having a sub-stantial portion of the solvent removed therefrom.
The agitation is quite important and may be achieved by the use of an agitator of a particular configuration as described below in detail. The agitation improves heat trans-fer and facilitates cooling the solution, thereby increasing the rate of precipitation.
In general the polymers suitable for the practice of the present invention include any normally solid synthetic organic polymeric thermoplastic resin whose decomposition point is somewhat higher than 100C. Included are polyole-fins, vinyls, olefin-vinyl copolymers, olefin-allyl copolymers, polyamides, acrylics, polystyrene, cellulosics, polyesters, and polyhalocarbons.
Generally, the most suitable polyolefins for use in the present process include normally solid poly~ers of mono-alpha-olefins, which comprise from 2 to 6 carbon atoms, for example~ polyethylene, polypropylene, polybutene, polyiso-butylenes~ poly (4-methylpentene~ copolymers of alpha-olefins and the like.
Vinyl polymers suitable for use herein include polyvinyl chloride, polyvinyl acetate, vinyl chloride/vinyl acetate copolymers, polyvinyl alcohol and polyvinyl acetal.
Among the suitable olefin-vinyl copolymers are ethylene-vinyl acetate, ethylene-vinyl propionate, ethylene vinyl isobutyrate, ethylene-vinyl alcohol, ethylene-methyl acrylate, and the like. Olefin-allyl copolymers include ethylene-allyl alcohol, ethylene allyl acetate, ethylene-allyl acetone, ethylene-allyl benzene, ethylene-allyl ether, and the like.
Examples of some specific acrylic polymers are polymethyl methacrylate, polyacrylonitrile, poly-methyl-10~98 acrylate and polyethylmethacrylate. me polyamides suitable for use include polyhexamethylene adipamide, polyhexamethylene sebacamide, and polycaprolactam.
The present process is also useful for preparing powders from solutions of mixtures of thermoplastic polymers such as ethylene vinyl acetate/polyethylene, polyethylene/
polypropylene and the like.
The present process may also be used to produce powders from a solvent reaction system wherein the polymeric material is prepared in a solvent system~ such as for example the alpha-olefin polymers, as described in numerous patents such as U.S. 2,112,300; U.S. 3,113,115; U.S. 3,197,452;
Belgian Patent 538,782 and British Patent 994,416. CataLysts are the now well known "Ziegler" variety.
Ziegler catalysts, or more particularly, certain modified Ziegler catalysts, have been found to be especially useful for polymerizing alpha-olefins. For example, a titan-ium trichloride catalyst modified with aluminum chloride having the formula TiC13.1/3AlC13. Normally, this modified Ziegler catalyst is activated with a metal alkyl such as an aluminum alkyl, and preferably with an aluminum alkyl halide having the structural formula, R2AlX or R3A12X3~ wherein R is selected from the group consisting of alkyl radicals con-taining 1 to 12 carbon atoms or phenyl or benzyl radicals, and X is a halogen atom selected from the group consisting of chlorine, bromine or iodine.
A variety of monomers may be polymerized with the Ziegler type catalysts. Any unsaturated hydrocarbon corres-ponding to the general formula R=CH=CH2, wherein R is se-lected from the group consisting of an alkyl radical hav;ng Irom one to six carbon atoms, a phenyl radical, or an alkyl substituted phenyl radical can be used. Examples of specific unsaturated hydrocarbons which can be polymerized include alpha-olefins containing 3 to 8 carbon atoms, such as propyl-ene, butene, isobutylene, pentene, isoamylene, hexene, iso-hexenes, heptene, isoheptenes, octene, isooctenes and the like.
The preferred catalyst composition for the polymer-ization of propylene comprises a modified titanium trichlor-ide having the structural formula, TiC13.1/3AlC13, activated with diethyl aluminum chloride. Ratios of diethyl aluminum chloride and titanium trichloride of between 0.3:1 and 6:1 may be advantageously used. The presence of an alkali metal halide in an amount of between 0.5 to 10 mols of an alkali metal halide per mol of reduced titanium tetrahalide, and preferably a mol ratio of from 0.8 to 5 mols of an alkali metal halide, such as sodium chloride, per mol of reduced titanium tetrahalide can be used for improving catalyst ac-tivity.
The monomers may be polymerized at moderate temper-atures and pressures with the Ziegler type catalysts des-cribed above, generally at temperatures of 0 C. to 150C., with temperatures on the order of 25 C. to 80 C. being particularly useful. A solvent such as a paraffin or cyclo-paraffin having 3 to 12 carbon atoms, may be employed for the polymerizations, however, the olefin monomer is frequently used for this purpose. The polymerizations are preferably conducted under conditions that exclude atmospheric impur-ities such as moisture, oxygen and the like.
The pressure ranges from about atmospheric pressure to about several atmospheres with pressures in excess of about 500 psi rarely being employed.
After the polymer has been produced, the catalyst is deactivated by contacting the polymeric reaction mixture 1~)ti1~98 with a material which reacts with and deactivates the cata-lyst. Such materials include, for example, lower alcohols, acetone and water.
The term polyolefins includes those materials modi-fied with materials such as the unsaturated organic acids, for example, maleic acid, muconic acid, dimethyl muconic acid, acrylic acid, methacrylic acid, vinyl acetic acid, and the like. Generally the polyolefins may be modified by from 1 to 10 weight percent of the unsaturated acid. The modifica-tion has been observed to improve the surface adhering char-acteristics of the polyolefin polymers when they are employed as surface coatings; this is particularly true of the alpha-olefins, such as polypropylene. The modifying unsaturated acids may be incorporated into the polyolefins by intimately contacting the modifier with the polyolefin in a melt or solution of the polymer in the presence of a free radical source, such as an organic peroxide or by copolymerization with another monomer followed by neutralization or partial neutralization to yield an ionomer if desired.
In the process of the present invention it is pos-sible to employ graft polymers prepared by known methods in the art, e.g., those to be found in U.S. Patents 3,177,269;
3,177,270; 3,270,090; 3,830,888; 3,862,265; British 1,217,231; British 670,562 and the like.
The preferred modifying monomers which are grafted to the backbone are C3 to C10~ preferably C3 to C6 unsatur-ated mono- and polycarboxylic-containing unsaturated acids with preferably at least one olefinic unsaturation; anhy-drides, salts, esters, ethers, amides, and nitriles, thio, glycidyl, cyano, hydroxy, glycol and other substituted deriv-atives thereof.
Fxamples of such acids, anhydrides and derivatives 10~
thereof include maleic acid, fumaric acid, itaconic acid, citraconic acid, acrylic acid, glycidyl acrylate, cyano ethyl acrylate, hydroxy ethyl methacrylate, acrylic poly-ethers, acrylic anhydride, methacrylic acid, crotonic acid, isocrotonic acid, mesaconic acid, angelic acid, maleic an-hydride, itaconic anhydride, citraconic anhydride, sodium acrylate, calcium acrylate, magnesium acrylate and the like.
Other monomers which can be used either by them-selves or in combination with one or more of the carboxylic acids or derivatives thereof include C8 to C50 vinyl mono-mers such as monovinyl aromatic compounds, i.e. styrene, chlorostyrenes, bromostyrenes, alpha-methyl styrene and the like.
Other monomers which can be used are C8 to C50 vinyl esters and allyl esters, such as vinyl butyrate, vinyl laurate, vinyl stearate, vinyl adipate and the like, monomers having two or more vinyl groups, such as divinyl benzene, ethylene dimethacrylate, triallyl phosphite, dialkylcyanur-ate and triallyl cyanurate.
The process of the present invention is especially useful for grafted polymers prepared by grafting a polymer of a C2 to C8 mono-c~-olefin or its copolymers with acrylic acid in a special process. The polymers of C2 to C8 mono- ~-olefins are commonly referred to as polyolefins and for the purpose of this invention are to include copolymers of the C2 to C8 mono-alpha-olefins with each other and with other monomers as well as the homopolymers.
Polymers containing diolefins such as butadiene and isoprene are also suitable. The polyolefins are produced utilizing in most instances a Ziegler-type catalyst, but can also be produced by Phillips catalysts and by high pressure technology.
_ g _ 10f~14~8 Examples of suitable polyolefins, both plastic and elastomeric, include low or high density polyethylene, poly-propylene~ polybutene-l~ poly-3-methyl butene-l~ poly-4-methylpentene-l~ copolymers of monoolefins with other olefins (mono- or diolefins) or vinyl monomers such as ethylene-propylene copolymers or with one or more additional mono-mers, i.e. EPDM~ethyléne/butylene copolymer, ethylene/vinyl acetate copolymer, ethylene/ethyl acrylate copolymer, propyl-ene/4-methylpentene-1 copolymer and the like.
The term "copolymer~l includes polymers formed from two or more monomer constituents and substituted derivatives thereof.
The preferred polyolefins employed in the present invention contain propylene and/or ethylene, i.e. polypropyl-ene and polyethylene. The starting polymer used as a basematerial in the graft process will preferably have a melt index (MI) (ASTM D-1238-65T) of 1 to 40, preferably 5 to 40, and most preferably 5 to 10, or melt flow rate (MFR~ between about 0.1 to 50 and preferably 0.5 to 10, most preferably 2 to 5. These melt flow rates correspond approximately to vis-cosity average molecular weights of about 100,000 to 500,000.
The preferred monomers to be grafted to the C2 to C8 polyolefin and other polymers for use in the present in-vention are maleic anhydride, acrylic acid, methacrylic acid, glycidyl acrylate, hydroxy ethyl methacrylate and their deriv-atives. Others that can be used are described elsewhere herein. However, other monomers may be added in admixture with these such as maleic anhydride (MA), styrene, acid esters, salts and the like to form graft copolymers. MA
and styrene and MA and acrylic acid are preferred over MA
alone when polymer grafts of MA are desired.
The grafting reaction is initiated by a free-radi--- 10 _ cal initiator which is preferably an organic peroxygen com-pound. Especially preferred peroxides are t-butyl perbenzo-ate, dicumyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxy-3 hexyne (Lupersol 130), alpha, alpha'-bis (tert-butylper-oxy) diisopropyl benzene (Vulcup R or Percadox 14), or any free radical initiator having a 10-hour half-life tempera-ture over 30 C. or mixtures thereof. Generally, the higher the decomposition temperature of the peroxygen compound, the better. See ~p. 66-67 of Modern Plastics, November 1971, for a more complete list of such compounds.
The free radical initiator is used in amounts cor-responding to 0.005 to 5, preferably 0.02 to 2, most prefer-ably 0.02 to 1.0 weight percent based on polymer.
The monomer to be graft polymerized is used in amounts of 0.01 to 100~ preferably 0.05 to 50~ and most pre-ferably 0.1 to 25 weight percent of the base polymer.
Generally, the monomer and initiator are blended together and added simultaneously, except in the situation of a polyethylene or ethylene predominant copolymer. Illus-trative of the graft preparation is the grafting of acrylic acid onto polypropylene. Molten polypropylene is contacted with acrylic acid at 350 to 650F., preferably 400 to 550 F.
in the presence of a peroxide initiator. The initiator and acrylic acid are added as a liquid blend. The resulting graft copolymers have been appreciably degraded and changed in molecular weight as compared to the base polymer. The solvents employed are preferably paraffins or cycloparaffins having 5 to 12 atoms. Suitable solvents include n-pentane, isopentane, n-heptane, isooctane, cyclohexane, methylcyclo-* Trade Mark.
10~
hexane, nonane, and the like or mixtures of solvents. The solvent will generally contain from about 1 to 40 weight per-cent, more preferably about 5 to 20 weight percent of polymer based on the total weight of the solution.
About 15 weight % of the polymer is dissolved in the solvent, for example n-heptane, by heating at 100 to 140C. preferably in the range of 110 to 130C. under auto-genous pressure for 5 minutes to 2 or more hours, typically about 1 hour. Preferably the temperature is selected to maintain the pressure in the autoclave at less than 75 psig;
more preferably less than 50 psig.
The slurry is produced by cooling the solution, to a temperature below 90C. Polymer precipitation begins at about 90 C. and continues as the temperature is lowered, at a rate of 1 to 10C./minute, preferably about 5C/minute.
The temperature of the solution is lowered to about 50C.
Lower temperatures may be used but are not necessary, simi-larly temperatures from 20C. up to about 80C. are suitable for the final slurry temperature. It is readily apparent that at temperatures above 20 C., somewhat larger amounts of polymer will remain dissolved in the solvent, unless long precipitation periods are provided. In any event it is neces-sary to keep the residual polymer, which is dissolved in solu-tion, below the concentration which will produce strings as the solvent is atomized along with slurry particles. Up to a critical amount of polymer may be present in solution in the solvent without the formation of strings as the solvent is atomized into a vaporization zone where the solvent is partially vaporized.
Thus since it is desirable, and one of the objects of the present invention is to remove solvent from the slurry particles, operation of the present process should be carried out such that there is less than that amount of the polymer remaining in solution in the solvent than will inhibit forma-tion of droplets at the drying zone temperature. The amount of polymer which may remain in solution in a solvent which has a vapor pressure of 50 to 400 mm of mercury at the temper-ature of the drying zone is that amount which produces a vis-cosity in the solvent of no greater than 5 centipoise at the temperature of atomi~ation. The particular lower or final precipitation temperature will have to be determined for each solvent and polymer employed to achieve this result.
This can be easily done or may be available in standard tech-nical and engineering tables in regard to some combinations.
Lengthened precipitation periods may also be used to remove larger amounts of polymer from solution at a given tempera-- 15 ture.
The cooling and precipitation is conducted in an agitated solution. As noted above, this aids cooling and speeds precipitation. However, the nature of the agitation is quite critical. The prior art believed that shearing of solution encouraged the formation of polymer strings and thus sought to avoid all agitation to prevent this unde-sirable result. However, surprisingly it has been found that high shear does not result in strings.
The apparatus used in the present process to ob-tain high shear is shown in Fig. 2. It is a vessel which isfully baffled. Turbine agitators, typically 1/3 to 2/3 the diameter of the vessel have been used, operated with good results at from 20 to 300 rpm. ~atisfactory high shear agi-tation can be obtained with paddle diameter of from 30 to ~0 percent of the internal diameter of the vessel. Figs. 3 and 4 show a top view of the turbines in Fig. 2, The degree of shearing necessary to carry out the _ 13 -process is less than that which would be achieved if an emul-sion were produced. Emulsion of the precipitated polymer would involve too high a shear and is to be avoided. Thus the present shearing may be described as less than that necessary to produce an emulsion of polymer particles in the solvent, but by conventional chemical engineering practice the agitation is intense as measured by energy input per unit volume of liquid.
The precipitated particles form a slurry in the precipitation vessel. Thus slurry is removed (by gravity, pumping, pressure, screw, etc.) and atomized through a con-ventional nozzle or centrifugal atomizing wheel such as a Niro atomiæer into a vaporization zone, into which a drying gas is being fed at a temperature of 80 to 160 C., depending on the polymer and solvent, to produce powder particles leaving the vaporization zone at temperatures generally in the range of 30 to 50C. and having about 5 to 30 weight percent solvent still associated therewith. The damp powder is then dried to completion, for example, by fluidized bed, vibrating tray, tumbling or the like.
The vaporizing gas may be air; however, explosive mixtures may result with the powder, Preferably inert gases such as nitrogen, C02, or helium are employed.
Generally, the particles produced according to this method have a size of less than 100 microns, usually over 99%
of the particles are less than 75 microns.
Some powder, for example, propylene resins (poly-propylene, ethylene-propylene copolymers, blends of propyl-enes with ethylene-propylene rubber and high density poly-ethylene and acrylic acid grafted modifications thereof hav-ing melt flow rates of 2 to 80) tend to be made of 20 to 30~/
agglomerates as taken from the vaporization zone, with the 10~i14~l~
remainder being less than lO0 microns, e.g., less than 74 microns; the average size being about 30 microns.
The agglomerates are readily reduced to finer pow-der by attrition, for example, by impingement mill (particle on particle) or pin mill, such that the yield of particles of less than 100 microns approaches 99% or more. The milled agglomerate particles are irregularly spherical, but not sharply angular or elongated as with grinding.
The usual particle size in the absence of agglo~er-ation is less than 100 microns, however~ the powders are usually classified to remove any oversized particles, e.g., agglomerates, scale, trash etc. and to separate the powders for different uses.
It has also been found that additives such as stab-- 15 ilizer3 antioxidants, coloring agents and the like may con-veniently be added to the solution of polymer, before or during precipitation and slurry stages or during or after the drying step~ Soluble or disperible additives are very evenly distributed throughout the powders.
Fig. 1 represents a schematic embodiment of appa-ratus which could be employed to carry out the present pro-cess. A vessel 10 adapted for autogenous pressure is equipped with paddle 13 operated by a motor 14 and having baffles 12.
Conduit 11~ which may be a screw conveyor is provided to feed solid polymer~ usually as pellets into the vessel 10. Line 15 is provided for solvent entry. A heating exchange means 16 is provided in the vessel 10. The following description is given in regard to a batch operation, however, the present process may be carried out by continuous and semi-continuous operation.
The solid polymer pellets are fed via conduit 11 and the solvent is fed through line 15 in the desired ratios 1 into vessel 10. It should be appreciated that the functions
2 to be described in vessel 10 may be carried out in separate
3 vessels, with the same result, e.g " dissolution, crystalliza-
4 tion and precipitation. The mixture is heated by 16 to a temperature in the range of 90 to 140C. and stirred to dis-6 solve the polymer. The heating is discontinued and the solu-7 tion cooled while paddle 13 is rotated at 30 to 300 rpm's 8 preferably about 200 to 300 rpm's. If desired~ heat ex-9 changer 16 may be used to cool vessel 10.
The cooling and agitation is continued until the ll predetermined temperature at which less than that critical 12 amount of polyme~ is left in solution that otherwise would re-13 sult in strings and fibers. The remainder of the polymer is 14 crystallized and precipitated to form a slurry in the vessel 10. The slurry is removed from vessel 10, for example by 16 pumping via line 17 into n~ zle 18.
17 The slurried polymer is sprayed into spray cham~er 18 19. A heated atomizing gas may be fed through line 20 into 19 nozzle 18, for example entering chamber 19 through an orifice in the nozzle 18 concentric about the slurry orifice. The 21 atoD~izing gas for a two fluid nozzle is maintained below 90C.
22 temperature to keep the polymer from redissolving and to keep 23 the solvent from boiling too rapidly. The drying gas may be 24 heated to a temperature in the range of 80 to 160C. adjusted 2s for the solvent, and degree of dryness desired in the powders 26 leaving the spray chamber 19 through conduit 23, which may be 27 a gravity flow, conveyor, screw, pneumatic or the like. The 28 atomizing and drying gas is recovered and sent to cyclone 21 29 via line 22, where polymer fines are removed and returned via 24 into line 23. The recovered gas containing vaporized sol-31 vent is passed to scrubber/c~ndenser 25 via line 33, wherein 32 the solvent is recovered and returned via 26 to the solvent feed tank (not shown) for recycle or is otherwise employed.
The recovered atomizing gas passes through line 27 through heater 29 and hence is recycled into the spray chamber 19.
The damp powder from spray chamber 19 and cyclone 21 passes to a dryer 28, such as a fluidized bed where the remaining solvent is removed via line 30 to pass through cyclone 21 with the fines returning to dryer 28 via line 24 and vaporized solvent going to condenser 25.
The dried polymer powder goes via line 31 to class-ifier 32 where various sizes are separated for different util-izations.
The drying gas may be conveniently passed into the spray chamber by a disperser concentric with the centrifugal or pressure atomizer. The drying gas and powder are generally allowed to flow concurrently to the dryer outlet so that the slurry sees the hottest and dryest gases initially. The powder flow may be adjusted to be spiral and produce longer residence times in the spray chamber.
Generally the slurry is atomized through the nozzle under pressures of 5 to 50 psig but pressures just above that of the drying atmosphere are necessary for centrifugal atomiza-tion. The drying gas is fed at sufficient rates to not result in equilibrium limitations to drying. However, the rates must also be adjusted to provide suitable residence time.
The temperature of the drying gas and the rates of ~eed of the materials are preferably adjusted to produce a temperature in the vaporization zone, i.e., the spray chamber, in the range of 30 to 80 C. but certainly not so high as to soften the polymer particles and induce agglomeration~
As noted above substantially all of the particles are less than 75 microns in size. The average particle size according to the present process will be around 20 microns 1 and the particles will be æubstantially spherical, except as 2 noted above in regard to the agglomerated material. The 3 particles of this invention are predominately of a size suit-4 able for electrostatically sprayed coating, e.g., a range of about 5-60 micronsO
6 The details of the solution and precipitation ves-7 sel 106 are shown in Fig~ 20 Two turbines are employed, with 8 the upper turbine having flat blades 101 attached to hub 111 9 and the lower turbine having blad~s 102 at~ached to hub 112 at a 45 downward thrust~ Two baffles 103 and 104 are situ-ated at 180 from each other. The heat exchanger 105 is a 12 helical coil through which either a heating or cooling fluid 13 ma~ be passed depending on the sequence. The heat exchanger 14 is spaced away from the baffles by members 109 to allow free flow of the materials around the coils without clogging by 16 the precipitated polymer. The jacket of the vessel ma~ also 7 be heated and cooled for extra heat transfer areaO Similarly9 18 the baffles are spaced away from the vessel jacket 107 by 19 members 110 to prevent polymer building up-on the baffles.
The power used to rotate shaft 108 is typically 21 0.5 to 10 horse power per 1,000 gallons of material to be 22 agitated. This is gualitatively defined as "intense" agita-23 tion. The shear is high, due both to the intense agitaiion 24 and the turb~ne impellers which exhibit intense shearO Thus the problem observed in the prior æt attributing the produc-26 tion of polymer s~rings to shearing, is overcome by intensify-27 ing the degree of shear to a very high degree, short of emul-28 sification.
29 The terms def~ning agitation and shear are quali-tative, but nonetheless, do provide information to carry out 31 the present invention when coupled with the conditions of 32 operation. The optimum results of the present process are 106~498 1 obtained at 250 to 300 rpm.
2 EXAMPLES 1_4 3 In these examples acrylic acid modified (variable 4 acrylic acid content by weight) polyethylene, polyethylene and EVA were dissolved in heptane under autogenous pressure 6 at about 120C. and cooled to about 55C. under conditions 7 of high shear agitationO
8 The slurry was sprayed through a Niro centrifugal 9 atomizer having the drying gas entering the spray chamber through a disperser concentric about the atomization wheel 11 through which the slurry was atomized. S pherical particles 12 of which 99% were smaller than 75 microns were recovered.
13 The conditions of atomizing and the spray chamber are set 14 out in the Table below.
J~ ~ 00 ~ ' ~, ~I
ra o ;~
U
P~
a~ u o ,~
~ o ~ P
, ~ C~ . -a~ u O
o ,. P o o U~ o ~ ~ ~ ~ .
,~ O E~
z Lq C~
~ o C~ U -o o o o ~s ~ ~ ~ ~ C~
. E~ .
,~ ~ ~1 o o o o ~, E~
. . . U
. ~~ .,~ U
.~ ~
a) . . . o aJ ~ o ~ o ~U
U
~1 o ~ S~
O :~ ~ 0 c~ 0~1 ~d U
~ O
0 t~ ~ ~ O t) h td ~ ~
~ td 0 ~ U ~1 0 ~ ~ ~rl h ) c~ rl ~I P~ 13 h~ u ~5 C ~ a~ ~ ~ ~ P~
Gl U q~ C ~rl a) O < a~
P. a~ ~ 3,~
~ ~ ~ ~ ~ ~ P~
S~E-~ ~1 P ~ .~ ~ ~u S~ 0 3~rl ~u~ 0.,~ ,1.,1~,1 ~u ~ P~ 'u ~ o -1 ~'d ~ 0 ~ ~1 U~
~ ~ ~1 UlH ~::
The cooling and agitation is continued until the ll predetermined temperature at which less than that critical 12 amount of polyme~ is left in solution that otherwise would re-13 sult in strings and fibers. The remainder of the polymer is 14 crystallized and precipitated to form a slurry in the vessel 10. The slurry is removed from vessel 10, for example by 16 pumping via line 17 into n~ zle 18.
17 The slurried polymer is sprayed into spray cham~er 18 19. A heated atomizing gas may be fed through line 20 into 19 nozzle 18, for example entering chamber 19 through an orifice in the nozzle 18 concentric about the slurry orifice. The 21 atoD~izing gas for a two fluid nozzle is maintained below 90C.
22 temperature to keep the polymer from redissolving and to keep 23 the solvent from boiling too rapidly. The drying gas may be 24 heated to a temperature in the range of 80 to 160C. adjusted 2s for the solvent, and degree of dryness desired in the powders 26 leaving the spray chamber 19 through conduit 23, which may be 27 a gravity flow, conveyor, screw, pneumatic or the like. The 28 atomizing and drying gas is recovered and sent to cyclone 21 29 via line 22, where polymer fines are removed and returned via 24 into line 23. The recovered gas containing vaporized sol-31 vent is passed to scrubber/c~ndenser 25 via line 33, wherein 32 the solvent is recovered and returned via 26 to the solvent feed tank (not shown) for recycle or is otherwise employed.
The recovered atomizing gas passes through line 27 through heater 29 and hence is recycled into the spray chamber 19.
The damp powder from spray chamber 19 and cyclone 21 passes to a dryer 28, such as a fluidized bed where the remaining solvent is removed via line 30 to pass through cyclone 21 with the fines returning to dryer 28 via line 24 and vaporized solvent going to condenser 25.
The dried polymer powder goes via line 31 to class-ifier 32 where various sizes are separated for different util-izations.
The drying gas may be conveniently passed into the spray chamber by a disperser concentric with the centrifugal or pressure atomizer. The drying gas and powder are generally allowed to flow concurrently to the dryer outlet so that the slurry sees the hottest and dryest gases initially. The powder flow may be adjusted to be spiral and produce longer residence times in the spray chamber.
Generally the slurry is atomized through the nozzle under pressures of 5 to 50 psig but pressures just above that of the drying atmosphere are necessary for centrifugal atomiza-tion. The drying gas is fed at sufficient rates to not result in equilibrium limitations to drying. However, the rates must also be adjusted to provide suitable residence time.
The temperature of the drying gas and the rates of ~eed of the materials are preferably adjusted to produce a temperature in the vaporization zone, i.e., the spray chamber, in the range of 30 to 80 C. but certainly not so high as to soften the polymer particles and induce agglomeration~
As noted above substantially all of the particles are less than 75 microns in size. The average particle size according to the present process will be around 20 microns 1 and the particles will be æubstantially spherical, except as 2 noted above in regard to the agglomerated material. The 3 particles of this invention are predominately of a size suit-4 able for electrostatically sprayed coating, e.g., a range of about 5-60 micronsO
6 The details of the solution and precipitation ves-7 sel 106 are shown in Fig~ 20 Two turbines are employed, with 8 the upper turbine having flat blades 101 attached to hub 111 9 and the lower turbine having blad~s 102 at~ached to hub 112 at a 45 downward thrust~ Two baffles 103 and 104 are situ-ated at 180 from each other. The heat exchanger 105 is a 12 helical coil through which either a heating or cooling fluid 13 ma~ be passed depending on the sequence. The heat exchanger 14 is spaced away from the baffles by members 109 to allow free flow of the materials around the coils without clogging by 16 the precipitated polymer. The jacket of the vessel ma~ also 7 be heated and cooled for extra heat transfer areaO Similarly9 18 the baffles are spaced away from the vessel jacket 107 by 19 members 110 to prevent polymer building up-on the baffles.
The power used to rotate shaft 108 is typically 21 0.5 to 10 horse power per 1,000 gallons of material to be 22 agitated. This is gualitatively defined as "intense" agita-23 tion. The shear is high, due both to the intense agitaiion 24 and the turb~ne impellers which exhibit intense shearO Thus the problem observed in the prior æt attributing the produc-26 tion of polymer s~rings to shearing, is overcome by intensify-27 ing the degree of shear to a very high degree, short of emul-28 sification.
29 The terms def~ning agitation and shear are quali-tative, but nonetheless, do provide information to carry out 31 the present invention when coupled with the conditions of 32 operation. The optimum results of the present process are 106~498 1 obtained at 250 to 300 rpm.
2 EXAMPLES 1_4 3 In these examples acrylic acid modified (variable 4 acrylic acid content by weight) polyethylene, polyethylene and EVA were dissolved in heptane under autogenous pressure 6 at about 120C. and cooled to about 55C. under conditions 7 of high shear agitationO
8 The slurry was sprayed through a Niro centrifugal 9 atomizer having the drying gas entering the spray chamber through a disperser concentric about the atomization wheel 11 through which the slurry was atomized. S pherical particles 12 of which 99% were smaller than 75 microns were recovered.
13 The conditions of atomizing and the spray chamber are set 14 out in the Table below.
J~ ~ 00 ~ ' ~, ~I
ra o ;~
U
P~
a~ u o ,~
~ o ~ P
, ~ C~ . -a~ u O
o ,. P o o U~ o ~ ~ ~ ~ .
,~ O E~
z Lq C~
~ o C~ U -o o o o ~s ~ ~ ~ ~ C~
. E~ .
,~ ~ ~1 o o o o ~, E~
. . . U
. ~~ .,~ U
.~ ~
a) . . . o aJ ~ o ~ o ~U
U
~1 o ~ S~
O :~ ~ 0 c~ 0~1 ~d U
~ O
0 t~ ~ ~ O t) h td ~ ~
~ td 0 ~ U ~1 0 ~ ~ ~rl h ) c~ rl ~I P~ 13 h~ u ~5 C ~ a~ ~ ~ ~ P~
Gl U q~ C ~rl a) O < a~
P. a~ ~ 3,~
~ ~ ~ ~ ~ ~ P~
S~E-~ ~1 P ~ .~ ~ ~u S~ 0 3~rl ~u~ 0.,~ ,1.,1~,1 ~u ~ P~ 'u ~ o -1 ~'d ~ 0 ~ ~1 U~
~ ~ ~1 UlH ~::
5, ~r "~ i 'd - ~ 4 1 a) .
~ .
~d _I C~l . ~ ;C
1 The process was also applied to ethylene vinyl 2 acetate copolymer, ethylene vinyl acetate-acrylic acid co-3 polymer, polyethylene, polypropylene, and a blend of poly-4 ethylene and ethylenevinyl acetate-acrylic acid terpolymer.
Each polymer was generally employed as described above and
~ .
~d _I C~l . ~ ;C
1 The process was also applied to ethylene vinyl 2 acetate copolymer, ethylene vinyl acetate-acrylic acid co-3 polymer, polyethylene, polypropylene, and a blend of poly-4 ethylene and ethylenevinyl acetate-acrylic acid terpolymer.
Each polymer was generally employed as described above and
6 materials were produced in the MI range of from 0.5 to 40
7 with 99 ~ % of the powder of less than 74 mirrons and the
8 average particle size of about 20 microns as collected from
9 the spray drier. The powders did not require any dusting powders such as fumed sillca for handling. The powders re-11 mained handleable after packing Bulk density was about 12 0.45 grams/cc for the ethylene polymers and 0.3 grams/cc 13 for the propylene resins.
14 Polyethylene modified with 0.28% himic anhydride lS graft was also prepared in fine powder form as well as a 16 polyethylene - 0.29% himic anhydride graft that had been 17 esterified with an ethylene glycol ester and a polyethylene -18 2% glycidyl acrylate copolymer.
; 21 -
14 Polyethylene modified with 0.28% himic anhydride lS graft was also prepared in fine powder form as well as a 16 polyethylene - 0.29% himic anhydride graft that had been 17 esterified with an ethylene glycol ester and a polyethylene -18 2% glycidyl acrylate copolymer.
; 21 -
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for preparing powders of thermo-plastic polymers comprising dissolving 1 to 40 weight percent of thermoplastic polymer in a solvent of paraffin or cycloparaffin hydrocar-bons having 5 to 12 carbon atoms at a temperature greater than 100°C. up to about 165°C. under autogenous conditions, cooling said solution under autogenous condition to a temperature less than 90°C, subjecting said solution during said cooling to high shear agitation, precipitating said thermoplastic polymer during said cooling and high shear agitation, recovering a slurry of polymer particles and sol-vent, atomizing said slurry into a vaporization zone, feeding a drying gas at a temperature in the range of 80 to 180°C. into said vaporization zone, and recovering particulate polymer product having a substantial amount of said solvent removed therefrom.
2. The process according to claim 1 wherein the temperature of said solution is adjusted to maintain an auto-genous pressure of less than 100 psig.
3. The process according to claim 2 wherein said autogenous pressure is maintained at less than 50 psig.
4. The process according to claim 1 wherein said solvent is n-pentane, isopentane, isooctane, cyclohexane, methylcyclohexane, heptane, nonane or mixtures thereof.
5. The process according to claim 1 wherein the solvent is n-heptane.
6. The process according to claim 1 wherein the temperature of the drying gas is adjusted to maintain the temperature in the vaporization zone in the range of 30 to 80°C.
7. The process according to claim 6 wherein the drying gas has a temperature in the range of 90 to 160°C.
8. The process according to claim 6 wherein the drying gas is an inert gas.
9. The process according to claim 8 wherein the drying gas is nitrogen.
10. The process according to claim 1 wherein at least 5 weight % of said polymer is dissolved in said sol-vent.
11. The process according to claim 10 wherein said precipitating is continued until less than the amount of thermoplastic polymer which will inhibit formation of polymer droplets from said solvent is left in solution.
12. The process according to claim 1 wherein said recovered particulate polymer is dried to produce a powder, having substantially all of the particles thereof less than 100 microns.
13. The process according to claim 1 wherein said slurry is atomized through a centrifugal atomizer.
14. A process for preparing fine free flowing pow-ders of thermoplastic polymers comprising dissolving 5 to 20 weight % of said thermoplastic resin in a solvent of paraffin or cycloparaffin hydrocarbons having 5 to 12 carbon atoms at temperatures in the range of 100° to 140°C. under autogenous pressure, cooling said solution under autogenous pressure to a temperature less than 90°C.
intensely agitating said cooling solution to pro-vide high shear conditions therein, continuing said cooling to a temperature and for a sufficient period of time to precipitate said polymer and to leave less than the amount of said polymer in solution which will inhibit formation of droplets during atomization and drying, recovering a slurry of particulate polymer and sol-vent, atomizing said slurry through an atomizer into a vaporization zone, adding drying gas to said vaporization zone at a temperature in the range of 90 to 160°C. and at a rate to maintain the temperature of said vaporization zone in the range of 30 to 80°C., recovering a partially dry particulate polymer material from said vaporization zone and drying said partially dry particulate polymer material and recovering a powder.
intensely agitating said cooling solution to pro-vide high shear conditions therein, continuing said cooling to a temperature and for a sufficient period of time to precipitate said polymer and to leave less than the amount of said polymer in solution which will inhibit formation of droplets during atomization and drying, recovering a slurry of particulate polymer and sol-vent, atomizing said slurry through an atomizer into a vaporization zone, adding drying gas to said vaporization zone at a temperature in the range of 90 to 160°C. and at a rate to maintain the temperature of said vaporization zone in the range of 30 to 80°C., recovering a partially dry particulate polymer material from said vaporization zone and drying said partially dry particulate polymer material and recovering a powder.
15. The process according to claim 14 wherein the polymer comprises grafted polyolefins.
16. The process according to claim 15 wherein the said grafted polyolefin is acrylic acid grafted.
17. The process according to claim 15 wherein the said grafted polyolefin is glycidyl acrylate grafted.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/602,211 US4012461A (en) | 1975-08-06 | 1975-08-06 | Process for preparing polymer powders |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1061498A true CA1061498A (en) | 1979-08-28 |
Family
ID=24410431
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA257,898A Expired CA1061498A (en) | 1975-08-06 | 1976-07-27 | Process for preparing polymer powders |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4012461A (en) |
| JP (1) | JPS5219758A (en) |
| BE (1) | BE844961A (en) |
| CA (1) | CA1061498A (en) |
| DE (1) | DE2635301A1 (en) |
| GB (1) | GB1556424A (en) |
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|---|---|---|---|---|
| JPS6045646B2 (en) * | 1978-06-29 | 1985-10-11 | 住友化学工業株式会社 | Drying method for polyα-olefin |
| JPS5719026A (en) * | 1980-07-10 | 1982-02-01 | Mitsui Eng & Shipbuild Co Ltd | In-liquid granulator |
| DE3302495A1 (en) * | 1983-01-26 | 1984-07-26 | Basf Ag | METHOD FOR REMOVING PHYSIOLOGICALLY POSSIBLE SOLVENTS FROM POLYMERISATES CONTAINING CARBOXYL OR ACID ANHYDRIDE GROUPS |
| DE3302496A1 (en) * | 1983-01-26 | 1984-07-26 | Basf Ag, 6700 Ludwigshafen | METHOD FOR INCREASING THE EFFECTIVENESS OF HIGH MOLECULAR CROSSLINKED POLYCARBONIC ACIDS |
| US4734227A (en) * | 1983-09-01 | 1988-03-29 | Battelle Memorial Institute | Method of making supercritical fluid molecular spray films, powder and fibers |
| US4734451A (en) * | 1983-09-01 | 1988-03-29 | Battelle Memorial Institute | Supercritical fluid molecular spray thin films and fine powders |
| US4582731A (en) * | 1983-09-01 | 1986-04-15 | Battelle Memorial Institute | Supercritical fluid molecular spray film deposition and powder formation |
| DE3587822T2 (en) * | 1984-12-13 | 1994-10-27 | Morton Int Inc | Primer composition and process for making it. |
| US4855179A (en) * | 1987-07-29 | 1989-08-08 | Arco Chemical Technology, Inc. | Production of nonwoven fibrous articles |
| US5707634A (en) * | 1988-10-05 | 1998-01-13 | Pharmacia & Upjohn Company | Finely divided solid crystalline powders via precipitation into an anti-solvent |
| US5171827A (en) * | 1990-03-05 | 1992-12-15 | E. I. Du Pont De Nemours And Company | Particulate acicular para-aramide |
| US5009820A (en) * | 1990-03-05 | 1991-04-23 | E. I. Du Pont De Nemours And Company | Process of making acicular para-aramide particles |
| US5229041A (en) * | 1990-09-20 | 1993-07-20 | The John Hopkins University | Method of making microscopic particles containing imbedded fluorescent dyes |
| BR9307346A (en) * | 1992-11-02 | 1999-06-01 | Ferro Corp | Process for preparing coating materials |
| US5824732A (en) * | 1993-07-07 | 1998-10-20 | Alliedsignal Inc. | Process for producing coating compositions containing ethylene-acrylic acid copolymers with polyamide grafts as rheology modifiers |
| EP0707616B1 (en) * | 1993-07-07 | 1998-02-11 | AlliedSignal Inc. | Coating compositions containing ethylene-acrylic acid copolymers with polyamide grafts as rheology modifiers |
| US5981696A (en) * | 1994-06-14 | 1999-11-09 | Herberts Gmbh | Process for preparing coating powder compositions and their use for making coatings |
| MX9504934A (en) * | 1994-12-12 | 1997-01-31 | Morton Int Inc | Smooth thin film powder coatings. |
| WO1996035983A1 (en) * | 1995-05-10 | 1996-11-14 | Ferro Corporation | Control system for processes using supercritical fluids |
| US5766522A (en) * | 1996-07-19 | 1998-06-16 | Morton International, Inc. | Continuous processing of powder coating compositions |
| US6075074A (en) | 1996-07-19 | 2000-06-13 | Morton International, Inc. | Continuous processing of powder coating compositions |
| US6114414A (en) * | 1996-07-19 | 2000-09-05 | Morton International, Inc. | Continuous processing of powder coating compositions |
| US6583187B1 (en) | 1996-07-19 | 2003-06-24 | Andrew T. Daly | Continuous processing of powder coating compositions |
| US5993747A (en) * | 1997-06-25 | 1999-11-30 | Ferro Corporation | Mixing system for processes using supercritical fluids |
| US6054103A (en) * | 1997-06-25 | 2000-04-25 | Ferro Corporation | Mixing system for processes using supercritical fluids |
| US6184270B1 (en) | 1998-09-21 | 2001-02-06 | Eric J. Beckman | Production of power formulations |
| US6506847B1 (en) * | 2001-08-08 | 2003-01-14 | Basell Poliolefine Italia S.P.A. | Controlling the molecular weight of graft copolymers using polymerizable chain transfer agents |
| FR2833267A1 (en) * | 2001-12-11 | 2003-06-13 | Solvay | A method of recovering a polymer from a solution in a solvent also containing a heavy liquid by adding a non-solvent, spraying into droplets and evaporating the solvent using a gas such as water vapor |
| US20050106310A1 (en) * | 2003-07-02 | 2005-05-19 | Green John H. | Designed particle agglomeration |
| JP2010132808A (en) * | 2008-12-05 | 2010-06-17 | Tosoh Corp | Method of manufacturing polyolefin resin |
| WO2009139439A1 (en) * | 2008-05-15 | 2009-11-19 | 東ソー株式会社 | Polyolefin resin manufacturing method, polyolefin resin, and solution and film thereof |
| US20110250264A1 (en) | 2010-04-09 | 2011-10-13 | Pacira Pharmaceuticals, Inc. | Method for formulating large diameter synthetic membrane vesicles |
| RU2517496C1 (en) * | 2013-05-29 | 2014-05-27 | Константин Сергеевич Сахаров | Paper laminate (versions) |
| RU2520528C1 (en) * | 2013-05-29 | 2014-06-27 | Константин Сергеевич Сахаров | Paper laminate (versions) |
| RU2520520C1 (en) * | 2013-05-29 | 2014-06-27 | Константин Сергеевич Сахаров | Paper laminate (versions) |
| RU2520510C1 (en) * | 2013-05-29 | 2014-06-27 | Константин Сергеевич Сахаров | Paper laminate (versions) |
| RU2519468C1 (en) * | 2013-05-29 | 2014-06-10 | Константин Сергеевич Сахаров | Paper-layered plastic (versions) |
| RU2520521C1 (en) * | 2013-05-29 | 2014-06-27 | Константин Сергеевич Сахаров | Paper laminate (versions) |
| RU2518553C1 (en) * | 2013-05-29 | 2014-06-10 | Константин Сергеевич Сахаров | Paper-layered plastic (versions) |
| RU2518562C1 (en) * | 2013-05-29 | 2014-06-10 | Константин Сергеевич Сахаров | Paper-layered plastic (versions) |
| RU2518565C1 (en) * | 2013-05-29 | 2014-06-10 | Константин Сергеевич Сахаров | Paper-layered plastic (versions) |
| RU2517487C1 (en) * | 2013-05-29 | 2014-05-27 | Константин Сергеевич Сахаров | Paper laminate (versions) |
| EP3508515A1 (en) | 2018-01-09 | 2019-07-10 | SABIC Global Technologies B.V. | Process and apparatus for precipitation of poly(phenylene ether) |
| PL245748B1 (en) * | 2021-01-19 | 2024-10-07 | Politechnika Śląska | Method of preparing polymer superabsorbents |
| US20220380557A1 (en) * | 2021-05-20 | 2022-12-01 | Xerox Corporation | Polyoxymethylene microparticles and methods of production and use thereof |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3119801A (en) * | 1964-01-28 | Recovery of olefin polymers fkom | ||
| US3244687A (en) * | 1956-05-24 | 1966-04-05 | Coathylene Sa | Process for the production of dry, finely divided and fusible polyethylene powders |
| US3306342A (en) * | 1966-03-02 | 1967-02-28 | Goodrich Gulf Chem Inc | Fluid processes useful in precipitation of dissolved solids |
| US3563975A (en) * | 1969-06-12 | 1971-02-16 | Fredrick J Zavasnik | Recovery of polymer powders from pressurized solutions of polymer |
| US3882095A (en) * | 1970-09-03 | 1975-05-06 | Crown Zellerbach Corp | Process for forming polyolefin fibers |
| US3862265A (en) * | 1971-04-09 | 1975-01-21 | Exxon Research Engineering Co | Polymers with improved properties and process therefor |
| US3743272A (en) * | 1971-04-12 | 1973-07-03 | Crown Zellerbach Corp | Process of forming polyolefin fibers |
| PH10340A (en) * | 1971-06-03 | 1976-12-09 | Crown Zellerbach Int Inc | Synthetic papermaking pulp and process of manufacture |
| US3849516A (en) * | 1972-04-03 | 1974-11-19 | Exxon Research Engineering Co | Grafted polyolefins as stabilizer components in polyolefins |
| US3896196A (en) * | 1973-02-27 | 1975-07-22 | Glasrock Products | Method of producing spherical thermoplastic particles |
-
1975
- 1975-08-06 US US05/602,211 patent/US4012461A/en not_active Expired - Lifetime
-
1976
- 1976-07-26 GB GB31026/76A patent/GB1556424A/en not_active Expired
- 1976-07-27 CA CA257,898A patent/CA1061498A/en not_active Expired
- 1976-08-05 DE DE19762635301 patent/DE2635301A1/en not_active Withdrawn
- 1976-08-05 JP JP51093559A patent/JPS5219758A/en active Pending
- 1976-08-06 BE BE169619A patent/BE844961A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BE844961A (en) | 1977-02-07 |
| GB1556424A (en) | 1979-11-21 |
| JPS5219758A (en) | 1977-02-15 |
| DE2635301A1 (en) | 1977-02-17 |
| US4012461A (en) | 1977-03-15 |
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